Glass fiber is an inorganic fiber material and can be used to reinforce resins to produce composite materials with good performance. As a reinforcing base material for advanced composite materials, high-performance glass fibers were originally used mainly in the national defense industry, such as aeronautic, aerospace and military industry. With the progress of science and technology and the development of economy, high-performance glass fibers have been widely used in civil and industrial fields such as motors, wind blades, pressure vessels, offshore oil pipes, sports apparatus and auto industry.
Since the US developed S-2 glass fiber, different countries have competed in developing high-performance glass fibers with various compositions, e.g. R glass fiber developed by France, HiPer-tex glass fiber developed by the US and high-strength glass fiber 2# developed by China. The original high-performance glass compositions were based on an MgO—Al2O3—SiO2 system and a typical solution was S-2 glass of the US. However, the production of S-2 glass is excessively difficult, as its forming temperature is up to about 1571° C. and its liquidus temperature up to 1470° C. and therefore it is difficult to realize large-scale industrial production.
Thereafter, in order to decrease the melting temperature and forming temperature of glass to better satisfy the needs of large-scale production with refractory-lined furnaces, large foreign companies successively developed high-performance glasses based on an MgO—CaO—Al2O3—SiO2 system. Typical solutions were R glass of France and HiPer-tex glass of the US, which were a trade-off for production scale by sacrificing some of the glass properties. However, as these designed solutions were too conservative, especially the content of Al2O3 was kept more than 20%, preferably 25%, the production of glass remained highly difficult. Although small-scale production with refractory-lined furnaces was achieved, the production efficiency was low and the cost performance ratio of the products was not high. The traditional R glass is difficult to fiberized as its forming temperature is up to about 1410° C. and its liquidus temperature up to 1330° C., which causes difficulty in attenuating glass fiber and consequently in realizing large-scale industrial production.
In addition, there is an improved type of R glass fiber, and its strength and modulus are much higher than those of the traditional E glass fiber and its melting and forming conditions are better than those of the traditional R glass fiber. However, this type of R glass has a high risk of devitrification. Meanwhile, since too much Li2O is introduced, not only the chemical stability of the glass is decreased, but also its raw material cost gets significantly higher. Therefore it is also not suitable for large-scale industrial production.
The High-strength 2# glass fiber mainly comprises SiO2, Al2O3 and MgO, and certain amounts of Li2O, B2O3, CeO2 and Fe2O3 are also introduced. It also has high strength and high modulus and its forming temperature is only about 1245° C. and its liquidus temperature is 1320° C. Both temperatures are much lower than those of S glass fiber. However, since its forming temperature is lower than its liquidus temperature, which is unfavorable for the control of glass fiber attenuation, the forming temperature has to be increased and specially-shaped tips have to be used to prevent a glass crystallization phenomenon from occurring in the fiber attenuation process. This causes difficulty in temperature control and also makes it difficult to realize large-scale industrial production.
Owing to the restriction in production conditions, i.e., the unsuitability for large-scale industrial production, the high-performance glass fibers available at present is very expensive both for their high production costs and selling prices, which lead to a very small output of these fibers. They are utilized only in a limited application fields such as aeronautic, aerospace and military, and cannot satisfy the large demands from the new fields such as high-power wind blades, high-pressure pipelines and pressure vessels.